Sauce: In saucepan, heat water & crushed rock sugar until sugar melts. Add pickle juice, soy sauce, vinegar & diced pickles. Bring to boil, stirring constantly. Restir cornstarch paste, and dribble it into boiling sauce, until sauce has consistency of thin pancake batter. Remove from heat. Reserve in saucepan. Preparation: Slice cod filet across the grain about 1/2" thick, keeping slices in position. Cut leafy fringes off of cabbage (save for your stock pot). Cut cabbage stalks lengthwise into pieces to match fish slices. Insert cabbage slices between each slice of fish. Hold together and slice fish & cabbage in half. Using broad side of cleaver, lift fish & cabbage, as is, onto 10" oval serving dish. Sprinkle ginger and sesame oil on fish. Steaming: About 15 minutes before serving time, bring water in steamer to boiling. Steam fish platter in steamer for 7-10 minutes, until fish turns milky white. Meanwhile, reheat sauce. Remove fish from steamer and pour off any water. Pour sauce unevenly over fish so it is only partly covered. Garnish with green onions. Serve.